The present invention relates to heart assist devices, systems and methods.
Currently the only real options for improvement of end-stage heart failure are medical therapy, left ventricular assist devices (LVADS) and transplantation. ACE (Angiotensin Converting Enzyme) inhibitors unload the heart and prolong survival. LVADs pump blood and significantly improve life style and survival, but are complicated to implant, maintain and remove, with relatively high complications relating to bleeding, infection, thromboembolism, and device malfunction.
The transplant rate has stabilised at approximately 2,300 per year in the USA, being limited by organ availability. Transplantation achieves a 75% five year survival rate and a 65% ten year survival rate with significant improvements in functional class.
The number of people awaiting heart transplantation is steadily increasing and they are a sicker group, with increasing numbers requiring hospitalisation, intravenous ionotropes. short-term percutaneous trans-femoral intra-aortic balloon pumping and/or LVAD implantation.
The Institute of Medicine has estimated that by the year 2010, up to 70,000 patients will be candidates for permanent mechanical circulatory support systems.
Over the last ten years, LVADs have been well proven to save lives, acting as bridges to transplantation for critically ill patients. Recently, LVADs have been considered as alternatives to transplantation, and very recently, have been explanted in a few patients who have shown recovery. This latest realisation is starting to gather a lot of interest as researchers focus on recovery of the failing heart. LVADs totally unload the left ventricle and many believe that the heart will then recover. Moreover there is evidence beyond the few patients in whom devices have been removed that there is reversal in markers of heart failure. On the other hand, others have described an increase in myocardial fibrosis which raises a question of whether the heart is being unloaded too much.
The intra-aortic balloon pump (IABP) was first proposed in the 1960s as a method of partial support for the acutely failing heart, for example, after heart surgery or heart attack. It was built as a long thin catheter [10-14 Fr] with an elongated balloon at its tip [volume 30-40 ml]. The balloon was inserted via the femoral artery and inflated and deflated in counterpulsation with the heart beat. Inflation in diastole causes a diastolic pressure augmentation and increases coronary artery blood flow and deflating in systole (triggered by the R wave of the ECG) reduces the afterload, or the pressure head against which the left ventricle has to eject blood. Early investigators determined that the best and most efficient balloon position was closest to the heart, i.e., in the ascending aorta. However, in recent times, the balloon is positioned via the femoral artery in the descending aorta for short term (1-10 days) use. There is substantial proof beyond doubt that counterpulsation works very well in the short-term to assist hearts to recover when drugs (ionotropes etc.) are insufficient or inappropriate to support the cardiovascular system.
Intra-aortic balloon heart pumps operating in counterpulsation assist the heart function. When inflated, the balloon propels blood peripherally from within the aorta to improve blood circulation in the patient. Moreover, more blood is forced into the coronary arteries to help nourish and strengthen the heart muscle. However, the balloon comes into direct contact with the blood flowing into the aorta, which can cause damage to the blood cells and there is a risk of thromboembolism. In addition. current intra-aortic balloon pump systems are inflated by means of a tube passing through the body, the tube connecting the balloon to an external compressor. The opening for the tube to enter the body provides a possible site of infection or other injury. The tube is typically inserted into a groin vessel, the femoral artery, and there is a high risk of associated leg complications. Further, the patient is bedridden and cannot mobilize. Additionally, the use of a gas to inflate the balloon is not an entirely safe operation since any leakage of gas from the balloon into the blood stream could cause an air embolus.
Aortic compression (periaortic diastolic compression) has been described as a means to increase coronary blood flow. For example, U.S. Pat. No. 4,583,523 describes an implantable heart assist device including an elongated assembly extending transversely between the ribs of a patient from the rib cage to the aorta of the heart to be assisted. The assembly includes an aorta compressing device at the front end and a mounting device at the rear end thereof to support the device from the ribs of the patient. A motive device actuates and deactivates the compressing device alternatively to help pump blood through the aorta in a counterpulsation mode of operation. Although this device has advantages for many applications, it does require relatively complicated surgery to implant/explant the device, particularly in regard to the need to mount the device, including its motive means, to the ribs of the patient. Moreover the mounting arrangement and motive means of the device have to be positioned outside the rib cage, making the presence of the device more noticeable to the patient. There is also substantial risk of infection with the device coming through the skin. Furthermore, because the device is attached/mounted to the ribs, there may be shear stresses on the aorta as the rib cage moves with inspiration/expiration. These stresses may cause untoward damage of the aorta.
U.S. Pat. No. 4,979,936 discloses an autologous biologic pump in the form of an apparatus using skeletal muscle formed into a pouch which then surrounds a collapsible. shape-retaining bladder. The bladder is connected to a second bladder enclosed in a sheath around a portion of the aorta. The bladders are filled with a fluid such that when the skeletal muscle contracts in response to an electrical stimulation. the fluid is forced from the first bladder into the second bladder sheathed around the aorta, expanding that second bladder and forcing the aorta to compress. Although this approach may be useful in some circumstances, it is doubtful that it is suitable for long term in that the muscle function would probably degrade over time. Furthermore, the muscle has to be xe2x80x9ctrainedxe2x80x9d for many weeks before the device can be relied on to assist blood circulation.
WO 99/04833 discloses a cardiac ventricle aid device which is implanted in the abdominal cavity with an aorta sleeve tube placed on, or inserted in, the descending aorta. A disadvantage of the disclosed device is it has a separate actuator and compliance chamber and its implantation is thus complicated. Another disadvantage is it is difficult to securely mount the device components to a structure in the abdominal cavity that is capable of supporting its weight. A further disadvantage is a number of vertebral arteries stem from the descending aorta which can be damaged during the implantation of the device.
It would be desirable to have a heart assist device that could be quickly and totally implanted in a relatively easy manner and with minimum trauma to the patient and to allow ambulation with low risk of complications. Also desirable would be a heart assist device that allows partial unloading of the heart longterm, augmenting the cardiac output of the native heart, and possibly allowing substantial recovery of the heart so that the device could be weaned. Moreover. it would be desirable for such a device to have no blood contacting surfaces. and not require cardiopulmonary bypass to implant the device. In a small proportion of patients however there will exist aortic disease making a periaortic device unsuitable. In these patients it would be desirable to be able to apply the same aortic counterpulsation, but with a device that replaces the ascending aorta. For this reason reference in this specification to xe2x80x9ccompression of the aortaxe2x80x9d includes compression of a prosthesis replacing a resected portion of the aorta. Such a device would require cardiopulmonary bypass and would be blood contacting, but has the same advantages of allowing partial unloading of the heart longterm, augmenting the cardiac output of the native heart, and possibly allowing substantial recovery of the heart so that the device could be weaned.
It is an object of the present invention to satisfy one or more of the above desirable criteria.
In a first aspect, the present invention provides a heart assist device adapted for implantation into a patient, the device including
a) an aortic compression means is so shaped and dimensioned that it is adapted, when actuated, to compress the ascending aorta of a patient;
b) a fluid reservoir; and
c) an electrically powered pump means adapted to pump a fluid from the fluid reservoir to the aortic compression means so as to actuate the aortic compression means at least partly in counterpulsation with the patient""s heart,
the fluid reservoir and the pump means are so shaped, dimensioned and interconnected that they are adapted to be wholly positioned within the right chest cavity of the patient.
In a second aspect, the present invention provides a heart assist device adapted for implantation into a patient, the device including:
a) an aortic compression means which is curved along its length so as to substantially replicate the curve of the ascending aorta adjacent to the aortic compression means and is so shaped and dimensioned that it is adapted, when actuated, to compress the aorta of a patient;
b a fluid reservoir; and
c) pump means adapted to pump a fluid from the fluid reservoir to the aortic compression means so as to actuate the aortic compression means at least partly in counterpulsation with the patient""s heart,
the fluid reservoir and the pump means are so shaped, dimensioned and interconnected that they are adapted to be wholly positioned within the chest cavity of the patient.
In a third aspect, the present invention provides a heart assist device adapted for implantation in a patient, the device including:xe2x80x94
a) an aortic compression means which includes an inflatable cuff and is so shaped and dimensioned that it is adapted to encircle and, when actuated, compress the aorta of a patient, the cuff being substantially C-shaped and including two free ends that are adapted to overlap when the cuff is placed around the aorta;
b) a fluid reservoir; and
c) pump means adapted to pump a fluid from the fluid reservoir to the aortic compression means so as to actuate the aortic compression means at least partly in counterpulsation with the patient""s heart,
the fluid reservoir and the pump means are so shaped, dimensioned and interconnected that they are adapted to be wholly positioned within the chest cavity of the patient.
In a fourth aspect, the present invention provides a heart assist device adapted for implantation in a patient, the device including:xe2x80x94
a) an aortic compression means which includes an inflatable cuff and is so shaped and dimensioned that it is adapted to substantially encircle and, when actuated, compress the aorta of a patient, the cuff having two free ends, one of which includes an elongate tongue adapted for suturing or other connection in an overlapping relationship to the other end to retain the cuff in place around the aorta:
b) a fluid reservoir; and
c) pump means adapted to pump a fluid from the fluid reservoir to the aortic compression means so as to actuate the aortic compression means at least partly in counterpulsation with the patient""s heart,
the fluid reservoir and the pump means are so shaped, dimensioned and interconnected that they are adapted to be wholly positioned within the chest cavity of the patient.
In a fifth aspect, the present invention provides a heart assist device adapted for implantation in a patient, the device including:xe2x80x94
a) an aortic compression means which, when actuated, compress the aorta of a patient;
b) a fluid reservoir; and
c) pump means adapted to pump a fluid from the fluid reservoir to the aortic compression means so as to actuate the aortic compression means at least partly in counterpulsation with the patient""s heart,
the fluid reservoir and the pump means are so shaped, dimensioned and interconnected that they are adapted to be wholly positioned within the chest cavity of the patient and the pump means and the fluid reservoir are provided in a fluid filled substantially air-tight housing.
In a sixth aspect, the present invention provides a heart assist device adapted for implantation in a patient, the device including:xe2x80x94
a) an aortic compression means adapted, when actuated, to compress the ascending aorta of a patient;
b) a liquid reservoir;
c) a pump means adapted to pump a liquid from the liquid reservoir to the aortic compression means so as to actuate the compression means, the liquid reservoir and the aortic compression means being adapted to be positioned in close juxtaposition with one another within the chest cavity of the patient, and
d) means to sense the pressure in the liquid in the absence of aortic compression and alter the sensed pressure to a predetermined pressure
In a seventh aspect, the present invention provides an aortic compression means for use in a heart assist device, the aortic compression means including:
a) an elastic inflatable cuff adapted to be placed about the ascending aorta of a patient; and
b) a flexible, substantially inelastic, sheath adapted to extend around the cuff and at least assist in retaining it in position on the aorta,
wherein the aortic compression means is curved along its length so as to substantially replicate the curve of the ascending aorta adjacent to the aortic compression means.
In a eighth aspect, the present invention provides an aortic compression means for use in a heart assist device, the aortic compression means including:
a) an elastic inflatable cuff adapted to be placed about the ascending aorta of a patient; and
b) a flexible, substantially inelastic, sheath adapted to extend around the cuff and at least assist in retaining it in position on the aorta,
wherein the cuff is substantially C-shaped and includes two free ends that are adapted to overlap when the cuff is placed around the aorta.
In a ninth aspect, the present invention provides an aortic compression means for use in a heart assist device. the aortic compression means including:
a) an elastic inflatable cuff adapted to be placed about the ascending aorta of a patient; and
b) a flexible, substantially inelastic, sheath adapted to extend around the cuff and at least assist in retaining it in position on the aorta,
wherein the cuff is substantially C-shaped and includes two free ends, one of the free ends includes an elongated tongue adapted for suturing or otherwise connected in an overlapping relationship to the other end to retain the device adjacent the aorta.
In a tenth aspect, the present invention provides a heart assist device including:
a) an aortic compression means adapted by its shape and dimensions to be placed around the ascending aorta of a patient; and
b) an actuation means to periodically actuate the aortic compression means in at least partial counterpulsation with the heart,
wherein the aortic compression means and the actuation means are placed wholly within the right chest cavity of the patient.
In an eleventh aspect, the present invention provides a heart assist device adapted for implantation wholly into a bodily cavity of a patient, the device including:
a) an aortic compression means adapted, when actuated, to compress an aorta of a patient;
b) a housing with an exterior surface;
c) a fluid reservoir in the housing, the fluid reservoir having a flexible exterior surface forming part of the housing exterior surface; and
d) a pump means adapted to pump a fluid from the fluid reservoir to the aortic compression means so as to actuate the aortic compression means at least partly in counterpulsation with the patient""s heart,
wherein the fluid reservoir flexible exterior surface is adapted to contract during aortic compression and expand in the absence of aortic compression and is further adapted to be positioned substantially adjacent a flexible organ in the patient""s bodily cavity.
Preferably, the bodily cavity is the thoracic cavity and the organ is the lung.
In a further aspect, the present invention provides an implantable system for assisting the functioning of the heart of a subject, the system including:
an implantable device for assisting the functioning of the heart of a subject, including:
means for externally engaging and compressing the aorta;
motive means responsive to control signal(s) for actuating and de-activating the compressing means cyclically to help blood pump through the aorta, wherein the compressing means and the motive means are fully implantable within the thoracic cavity of the subject and wherein the compressing means and/or motive means include means adapted for attachment to the aorta and/or surrounding tissue within the thoracic cavity of the subject;
sensing means adapted for sensing the heart and generating sensing signals;
control means responsive to the sensing signals for generating the control signal(s); and
a power source for providing power to the motive means.
The device of the invention may operate in countersynchronisation to the heart (counterpulsation).
An advantage of the device and system of the present invention is that the risk of limb ischemia associated with conventional IAB systems is avoided because there is no blood contact with the device whatsoever. Patient ambulation is also possible. Additionally the implantation technique used for the device of the invention is less invasive than those required for other devices. In particular, compared to the arrangement taught in U.S. Pat. No. 4,583,523, the device of the present invention provides a better outcome in term of reduced risk of infection, cosmesis and ease of implant and explant.
A further advantage of the device and system of the present invention is that there is little risk to the patient in the event of device failure. The device has the great advantage of being able to be weaned and turned off in the event of cardiac recovery. This is simply not possible with known LVADS. Furthermore if the heart shows signs of relapsing back into failure, the device can be switched back on.
The compressing means of the device of the present invention preferably includes a preshaped balloon cuff for wrapping around a portion of the aorta. Preferably, the balloon is configured longitudinally to fit the curve, that of a circular or oval arc, of the ascending aorta. In a particularly preferred form of the device of the present invention, the cross-section of the cuff is C-shaped, allowing wrapping of the cuff with some overlap around the aorta. Preferably, the cuff is shaped such that it does concentrically compress the length of enclosed aorta and spreads the compression forces evenly, reducing any wear or fatigue on any one part of the aorta. The balloon cuff is enclosed within a flexible and non-elastic outer sleeve. The sleeve has an elongated xe2x80x9ctonguexe2x80x9d on one arm of the C-shaped cuff and this is passed around the aorta to be secured by suturing or other means on the outer aspect of the other arm of the C-shaped cuff. This arrangement stops the balloon inflation force from going outwards. Furthermore, the preshaped cuff and flexible sleeve are particularly designed to create a snug fit and low profile on the aorta, to reduce damage to the aorta and surrounding structures, and to create maximum efficiency of the device.
In a preferred form of the invention, the device is adapted for compression of the ascending aorta. An upper mid-line sternotomy provides easy surgical access to the ascending aorta and has the further advantage of not being very painful for the patient. A minimum incision is required in this procedure. In this mode of use of the device of the invention, the compressing means is preferably adapted to squeeze approximately 15-25 ml of blood from the ascending aorta in each compression cycle.
The cuff has a single inlet/outlet port for the fluid to move to inflate/deflate the balloon. The fluid used is preferably liquid, such as water or saline, as this is noncompressible and less likely to leak compared to gas. Furthermore, using a liquid allows a fully implantable device so that the patient can mobilize easily. The port and connecting tube to the motive means is of sufficient diameter and length to allow rapid emptying and filling of the cuff without generating too high compression pressures. The fluid must move within 0.15 sec for effective counterpulsation action. The compressive force emptying the cuff is the force exerted by the compressed aorta. This approximately 100 mmHg. A tube lumen of approximately 1 to 1.5 cm with a length of 3 to 8 cm allows 17 to 25 ml fluid to pass down a gradient of 100 mmHg in less than 0.15 sec. The compressive force filling the cuff is generated by the motive means, and this pressure gradient is approximately the same ie the motive means generates approximately 200 mmHg to allow the fluid to shift into the cuff in less than 0.15 sec.
The port more preferably has a trumpet-shaped or flanged opening into the cuff to spread the fluid more evenly into the balloon during inflation and to assist more rapid deflation. There may be a diffuser mounted within the lumen of the port to reduce the fluid force on the balloon cuff during inflation.
Preferably, the motive means drives the fluid via a fluid filled sac contained within the motive means. The motive means of the device of the invention may be any means that is capable of cyclically compressing and decompressing the fluid sac. The motive means may be a mechanical or an electromechanical device. The motive means may be an electric motor/cam arrangement. The motive means may include spring mounted arms driven by a pulse of power to hinged solenoids or the like to drive the pressure plates towards each other and thereby compress the aorta. An example of a suitable motive means is an adaptation of the solenoid actuator described in U.S. Pat. No. 4,457,673, the relevant disclosure of which is incorporated herein by reference. The motive means may also be based on that used in the Novacor N1OO Left Ventricular Assist System.
The motive means is preferably enclosed in an air-tight housing. The housing may have a flexible portion that allows for the fluid shift from the motive meansxe2x80x94the flexible portion is presented toward the lung tissue and can thus move back and forth. More particularly the motive means is fully implanted within the thoracic cavity and a pressure compliance membrane xe2x80x9cinterfacesxe2x80x9d with the lung surface. Alternatively the housing may be rigid and when the motive means is activated and the fluid sac compressed, a small vacuum is created within the housing. This vacuum has the advantage of increasing the pressure gradient for subsequent emptying of the cuff, to make emptying more rapid. The level of vacuum could be adjusted by accessing a transcutaneous gas reservoir linked to the housing. A final alternative is to have a external gas line from the motive means to allow gas exhaust, eliminating the need for a compliance chamber, but introducing a percutaneous line that has an increased risk of infection.
The motive means may be designed so that in the event of failure, it automatically goes into xe2x80x9coffxe2x80x9d with the fluid sac filled so that the aorta is not compressed, thus minimising risk to the patient.
The motive means may include or be associated with means for detecting speed and completeness of cuff filling and emptying, and of monitoring the fluid pressure within the connector tube, means for measuring arterial blood pressure or flow. The motive means may also act to record the ECG, having electrodes positioned on the housing or as separate wires attached to body tissues.
The means adapted for attachment to the aorta and/or surrounding tissue of the subject may be any suitable means. For example, the attachment means may be adapted for suturing and/or gluing the compressing means or motive means to the aorta or the surrounding tissue within the chest cavity. The attachment means may be suturing tabs. The attachment means may be apertures allowing ingrowth of tissue and/or surface portions adapted to promote tissue growth into or onto the compressing means and/or the motive means so as to hold the device in position relative to the aorta. For example, the cuff may have a plurality of holes through which the cuff may be sutured to the aorta. The cuff may also have holes or slits to accommodate coronary artery bypass grafts to the ascending aorta. The motive means will sit within the chest cavity, preferably the right thoracic cavity, between the mediastinum and the right lung.
The sensor means may be means detecting a selected physiological event associated with heartbeat. The sensor means may be any means for producing an ECG. Means for detecting the action potentials of the cardiac muscles, for example electrodes, are well known to those skilled in the art and will not be described in detail here.
The control means may be any means capable of providing an output to actuate the motive means in response to signal(s) providing the sensor means.
The control means may provide signals to the motor means to countersynchronise compression of the aorta with the heart beat to provide counterpulsation, for example, aorta compression may commence with aortic valve closure (ventricular diastole), whilst aorta release occurs just prior to contraction/ejection (ventricular systole).
The power means may be an internal and/or external battery, or TET (transcutaneous electronic transfer).
De-activation of the compressing means may be timed to the R wave of the ECG and may be adapted for adjustment either manually or automatically. The dicrotic notch on the arterial pressure wave may provide the signal for actuation of the compressing means.
In yet a further aspect, the present invention provides a method for improving blood circulation in a subject, the method including implanting a device in accordance with the invention fully within the thoracic cavity of a subject, actuating the compressing means periodically in synchrony with the diastole period to compress the aorta; and alternating the period of actuation with periods of deactivation of the compressing means thereby allowing the aorta to return to its uncompressed shape.
The system and device of preferred embodiments of the invention allow relief/recovery from chronic heart failure whilst allowing the subject to move around freely without being constrained by a large external pumping device.